INSECTS AND HUMAN DISEASE 137 



tion, have been proved, beyond a doubt, to be the carriers 

 of the various diseases with which they are associated. 

 There remains one important problem which deserves men- 

 tion, namely, the probable transmission of pellagra by one 

 or more species of Simuliwm, popularly known as buffalo 

 gnats, or by some other closely related biting flies. The 

 history of pellagra and its probable connection with insect 

 life is of interest, quite apart from the question of what 

 insect will ultimately be proved to be the vector. Pellagra, 

 like malaria, yellow fever, and sleeping sickness, is essenti- 

 ally an endemic disease ; it is invariably associated with the 

 same ecological conditions. Just as malaria is associated 

 with stagnant water, so is pellagra linked to rapidly run- 

 ning streams. 



The disease itself was first recognised in Spain in 1735 

 by Dr Casal, and was then called mal de la rosa ; it affects 

 the skin and nervous system, causing, as its early name 

 implies, a red rash on the affected parts, the hands, neck, 

 etc., and often terminating fatally. It is probably rare in 

 England, but is endemic in the eastern districts of Scotland, 

 north of the Forth, and in the Shetland Islands, where it 

 was known as long ago as 1863. Till quite recently it was 

 thought that pellagra was contracted by eating maize that 

 had become stale and attacked by a fungus ; despite the 

 brilliant work of Dr L. Sambon, who first drew attention to 

 the fact that pellagra is probably carried by insects, and de- 

 spite the fact that pellagra occurs where maize is not eaten, 

 many still adhere to this belief. In certain districts of Italy 

 the disease is rampant, whole populations being affected in 

 some cases; in America it is spreading to an alarming extent. 



As the connection between insects and pellagra is at the 

 moment theoretical, with, it must be admitted, a strong 

 bias towards the probable, it is of interest to read 

 Dr Sambon's observations in the Venetian lagoon: 

 " Venice, with its urban population, is, as in the case of 

 all towns, entirely free from pellagra. The island of Lido, 



